World temperatures could soar by 4 degrees Celsius (7.2 degrees Fahrenheit) by the 2060s in the worst case of global climate change and require an annual investment of $270 billion just to contain rising sea levels, studies suggested on Sunday.

Such a rapid rise, within the lifetimes of many young people today, is double the 2 degrees C (3.6 degrees Fahrenheit) ceiling set by 140 governments at a U.N. climate summit in Copenhagen last year and would disrupt food and water supplies in many parts of the globe.

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Rising greenhouse gas emissions this decade meant the 2 degree goal was "extremely difficult, arguably impossible, raising the likelihood of global temperature rises of 3 or 4 degrees C within this century," an international team wrote.

The studies, published to coincide with annual U.N. climate talks in Mexico starting on Monday, said few researchers had examined in detail the possible impact of a 4 degrees C rise above pre-industrial levels.

"Across many sectors -- coastal cities, farming, water stress, ecosystems or migration, the impacts will be greater," than at 2 degrees, wrote Mark New of Oxford University in England, who led the international team.

One study, published in the British journal Philosophical Transactions of the Royal Society A, said temperatures could rise by 4 degrees C in the worst case by the early 2060s.

Other scenarios showed the threshold breached later in the century or not at all by 2100, raising risks of abrupt changes such as a loss of Arctic sea ice in summer, a thaw in permafrost or a drying out of the Amazon rainforest.